Use name to refactor CT event number filters

[Ed McDonagh]

No description provided.

[Ed McDonagh]

Refactored number of events into one function. Tidied up imports. Removed Py2 things. Refs #818

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[Ed McDonagh]

Adding ref #818 to changes - also adding ref #815 as it was missed in the PR (oops!)

→ <<cset 3bfba9db790d>>

[Ed McDonagh]

Tidying imports for Codacy. Refs #818

→ <<cset 7fe41b67a49c>>

[Ed McDonagh]

Refactored dap filters into one. Added doc strings. Refs #818

→ <<cset c07b846b6469>>

[Ed McDonagh]

Codacy issues. Refs #818

→ <<cset 85545c940741>>

[Ed McDonagh]

Merged in issue818refactorCTeventfilter (pull request #357)

Fixes #818

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